Proposal for mutating admission policies

[Joe Betz]

API Machinery experts,

I would like to collect feedback on KEP-3962: Mutating Admission Policies. This is a continuation of the validating admission policy feature currently in Alpha and targeting Beta in 1.28.

This approach attempts to make it easy to declare object mutations in CEL by combining CEL object instantiation and Server Side Apply merge strategies. It also proposes improvements to how mutations are ordered and validated to mitigate the risk of multiple mutating admission policies overwriting, undoing or otherwise clobbering each other's changes.

-Joe